#include <stdio.h>
#include <algorithm>
using namespace std;
const long long mod = 1000000007;
long long fpow(long long a, long long p)
{
a %= mod;
p = (p % (mod - 1) + mod - 1) % (mod - 1);
long long r = 1;
while (p){
if (p & 1) r = r * a % mod;
a = a * a % mod;
p /= 2;
}
return r;
}
long long inv[5005],p[5005],d[5005],bit[2][5005];
int main()
{
int n; scanf ("%d",&n);
inv[1] = 1;
for (int i=2;i<=n;i++) inv[i] = (mod - mod / i) * inv[mod % i] % mod;
long long pc=fpow(1000000000,-1);
for (int i=0;i<n;i++){
scanf ("%lld %lld",&p[i],&d[i]);
p[i] = p[i] * pc % mod;
}
long long sum = 0;
for (int i=0;i<=n;i++) bit[0][i] = bit[1][i] = 0;
bit[0][0] = 1;
for (int i=0;i<n;i++){
for (int j=i;j>=0;j--){
bit[1][j+1] = (bit[1][j+1] + bit[0][j] * p[i] % mod * d[i]) % mod;
bit[1][j+1] = (bit[1][j+1] + bit[1][j] * p[i]) % mod;
bit[0][j+1] = (bit[0][j+1] + bit[0][j] * p[i]) % mod;
}
}
for (int i=1;i<=n;i++){
long long add = bit[1][i] * inv[i] % mod;
if (i & 1) sum = (sum + add) % mod;
else sum = (sum + mod - add) % mod;
}
printf ("%lld\n",sum);
return 0;
}
